The present invention relates to a method for arranging conveyor-transported fragmentary particles of variegated shape into one or several adjacent rows of individual particles at as even intervals as possible for the purpose of, for example analysis and separation in which the fragments are analysed with regard to some property and separated into two or several products in accordance with predetermined separation criteria.
The invention also relates to an apparatus for carrying out the method according to the invention.
The analysis and separation of fragmentary particles, mentioned as one object of application of the invention, sets several requirements on the feeding of the particles. The analysis is performed either in air during the falling of the particle, or on the feeding device. In principle, only one fragment at a time may be, for the purpose of this operation, at the analysis and separation points which are of limited size. The analysis and separation times are in the order of 1-100 milliseconds, typically 5-30 ms, and the particles must be conveyed to the separation point in the same order as they arrived at the analysis point. The travel path and speed of the particle row must be as steady as possible. The particles must reach the analysis point and the separation point at as even intervals as possible, and these intervals should be as small as possible in order to achieve maximum capacity. Also, the apparatus must not break up the particles being handled, it must be reliable in operation in the surroundings in which it has been installed, and its price and operating costs must be as economical as possible.
Fragmentary particles have previously been arranged into a row of individual particles by means of, for example, vibrating feeders, which, however, have a disadvantage in a material travel speed which is too slow within the fragment-size range involved, the travel speed in the vibrating feeders used being in the reference experiments at maximum 0.2 m/s, although this speed can in certain cases be increased to above 0.5 m/s, e.g. to 0.8-2 m/s. However, it has been found that the speed optimal in terms of capacity in the case of the fragment-size ranges now in question is 0.8-1 m/s. Also, the deviation from the path by a fragment falling from a vibrating feeder is too great, partly owing to the vibratory motion continuing all the way to the end of the feeder, in which case the fragment at the point of falling from the end of the feeder may receive impulses having effect in different directions.
Profiled belts have also been used as devices forming a row of fragmentary particles, but they have a disadvantage in their limited capability to form a row. The flow of fragments from a preceding apparatus unit, such as a vibrating feeder, varies momentarily, and therefore the feeder may feed several fragments simultaneously, in which case, for example, angular rocks may remain one on top of the other or side by side on the profiled belt conveyor. Also, momentarily there may be no particles arriving from the conveyor, in which case a gap is formed in the row and full capacity is not achieved.
Also known is a grooved belt conveyor which "can be vibrated" by using an eccentric drive drum. In this case, however, in order to stabilize the paths of the particles, separate stabilizing devices are necessary onto which a fragment is dropped from the drive drum of the belt. Such a device is complicated and expensive, and in addition, the vibration remains weak owing to the dimensions of the drive drum. Also, the vibration is not focused specifically at the particle flow arriving on the belt, where it should be most effective.
The object of the present invention is therefore to provide a method and apparatus for arranging fragmentary particles into a row or adjacent rows of individual particles without the disadvantages present in the above-mentioned devices and methods.